Embodiments presented herein relate generally to infra-red imaging, and more specifically to transient thermographic inspection.
Thermographic inspection is the nondestructive testing of objects through imaging of thermal patterns on the object's surface. Thermographic inspection is often preferred to other nondestructive testing techniques such as ultrasonic inspection and radiographic inspection, for various advantages offered by thermographic inspection. Thermographic inspection is non-contact, non-intrusive, allows for detection of subsurface detects close to the surface, allows for inspection of large surfaces, and offers high speed inspection. One form of thermographic inspection is transient thermography. Transient thermography involves observing the temperature distribution on the surface of an object under test as it is subjected to a thermal transient such as a pulse of heat or a pulse of heat sink, and then allowed to return to ambient temperature. Any flaws present are detected as abnormalities in the surface temperature distribution during this thermal transient. Transient thermography is particularly well suited to the inspection of composite materials. The relatively low thermal conductivity of composite materials results in relatively long-lived thermal transients, therefore making the thermal transient easy to detect with a thermal camera.
Some known thermographic inspection techniques are operator dependent techniques, involving an operator to watch a thermal video of the object under test. The operator then observes the video for changes in contrast caused due to flaws within the object. Such techniques are skill intensive and require much manual effort. Automated thermographic inspection techniques also exist. Automated thermographic inspection uses a heat source such as a high intensity flash lamp to heat the surface of an object under test. An infra-red camera then takes a series of thermal images or thermograms of the object under test. The images are then post processed to identify features in the object under test.
Known automated thermographic inspection techniques use an infra-red camera driven at a constant frame rate. In other words, the infra-red camera is adapted to capture thermal images at fixed intervals of time. However, the thermal activity occurs at a non-linear rate. This causes too few thermal images being captured at the beginning of the thermal transient, when the thermal activity is high, and too many thermal images (with a large proportion being redundant images) being captured at the end of the thermal transient when the thermal activity is significantly slower. This causes very large data files that require a large buffer memory, a faster bus, and subsequently requires large disk space for storage and archival. These higher computing requirements increase the cost of the thermographic inspection system. Some techniques may partly address the storage problem by extracting thermal images from the large set of captured images. However, such techniques still require large buffers and fast busses to facilitate high speed image capture.
Therefore, there is a need for a thermographic inspection system that addresses these and other shortcomings associated with known solutions.